What are the origins of sourdough?

For a long time, the addition of sourdough was the only way to make bread rise. It is very difficult to date the discovery of leaven, but the earliest representations of it date back to the Old Egyptian Empire. Depending on the version, leaven may have been discovered by the Babylonians or the Hebrews. But the most frequently cited origin is that of Egypt: a person delayed cooking his cereal dough, and this, under the effect of fermentation, began to swell, thus creating the first leavened bread. The Egyptians, and before them the Sumerians, mastered fermentation: they made both beer and bread.